Mechanical drug and agent delivery devices are utilized in a wide range of applications including a number of biological applications, such as catheter interventions and other implantable devices used to create a therapeutic or other biological effect within the body. Often, such delivery devices take the form of radially expandable devices used to mechanically open an occluded or narrowed blood vessel. For example, inflatable non-elastomeric balloons have been utilized for treatment of body passages occluded by disease and for maintenance of the proper position of catheter-delivered medical devices, such as stents, within such body passages. With the use of drug carrying polymers applied to the stents to form drug eluting stents, such stents are placed within body lumens with drugs or agents embedded therein for release of the drug or agent within the body.
Some intervention balloon catheters are made to deliver a systemic bolus of liquid or gas that includes a drug, to a targeted tissue location within the body using an open catheter lumen or channel located at some length along the catheter shaft. Unfortunately, when such systemic delivery means are used to deliver a controlled volume of medication to a desired tissue location, a majority of the medication is lost to systemic circulation because of an inability of the drug to quickly penetrate local tissue. Generally, most liquid formulations containing a drug or agent that is delivered to the targeted tissue location by liquid bolus does not penetrate the tissue sufficiently at the targeted tissue location to result in a significant therapeutic effect, and is consequently washed away by body fluids. This systemic dilution substantially diminishes the effectiveness of the drugs or agents provided through such delivery devices, and increases the likelihood of a greater systemic effect caused by the large quantity of drug or agent washed into the bloodstream. To compensate for such delivery inefficiency, the dose of drugs or agents must be volumetrically increased in anticipation that they will be principally washed away before therapeutically effecting the localized or targeted tissue area. However, because of the risk of increased systemic effects and possibly toxic overload, the volume of the drugs or agents must not exceed that which can still be considered safe for exposure by systematic dilution and subsequent systematic distribution throughout the patient's body. The drug or agent used in such an intervention delivery method must be safe enough in its diluted state to be washed away to other parts of the patient's body and not have unwanted therapeutic or otherwise detrimental effects. There is a delicate balance between making the drugs or agents sufficiently concentrated to have therapeutic characteristics at the targeted tissue location, while also being sufficiently diluted to avoid harmful effects after being washed away into the body's systemic circulation.
Alternative to a systemic delivery, a local delivery of therapeutic agent can be administered. The local delivery can involve provision of a therapeutic agent using an applicator or as a portion of a coating on an implanted medical device. With provision of the drug or agent directly at the desired targeted tissue location, the systemic effects can be drastically reduced and the concentration of the drug or agent at the targeted tissue location can be substantially increased. One method for increasing the amount of drug at a targeted tissue location is to deliver the drug in relatively viscous configurations, such that when applied to the targeted tissue location, the drug or agent is not easily flushed away due to the adhesion of the viscous configuration to the tissue.
In accordance with certain configurations and embodiments for the local delivery of a therapeutic agent to a targeted tissue location, a balloon catheter can be utilized to transport a therapeutic agent, and then apply the therapeutic agent, to the targeted tissue location. However, in a collapsed or folded configuration, it can be difficult to evenly distribute the coating across the outer surface of the balloon, or provide a sufficient amount of coating on the exposed portions of the balloon surface. A more viscous coating can have a heavier drug load, but not evenly coat the collapsed or folded balloon, while a less viscous coating can penetrate into the folds of the collapsed or folded balloon, but may not have a high drug concentration.